docs: note that activateApp is also a roku command

Author: jlipps

README.md

@@ -98,6 +98,7 @@ await driver.executeScript('roku: pressKey', [{key: 'Home'}])
 |`roku: deviceInfo`||Get information about the Roku device|
 |`roku: getApps`||Get a list of apps installed on the device. The response will be a list of objects with the following keys: `id`, `type`, `subtype`, `version`, and `name`.|
 |`roku: activeApp`||Get information about the active app, in the same format as `roku: getApps`.|
+|`roku: activateApp`|`appId` (required), `contentId`, `mediaType`|Launch an app with the corresponding `appId`. Optionally include `contentId` and `mediaType` information (with the same properties as described above for the `activateApp` command)|
 
 ## Contributing